1. Field of the Invention
The present invention relates to a method for producing an electrophotographic photoreceptor and an apparatus used therefor. In particular, it relates to a method for producing an electrophotographic photoreceptor for obtaining electrophotographs utilizing the phenomenon that any selected area which has been converted to an insulator always maintains its pattern, and an apparatus used therefor. More particularly, it relates to a method for producing an electrophotographic photoreceptor which makes it possible to carry out copying repeatedly without one imagewise exposure for every one copying by simple steps of converting any selected area of a photoreceptor to an insulator, converting the pattern of this area, namely, the pattern formed by the insulator to electrostatic image, and utilizing this electrostatic image for copying, and to an apparatus used therefor.
2. Related Art Statement
Electrophotography is a technique which comprises exposing imagewise a selected partial area of the surface of photoreceptor with visible light to retain electrical charges in only unexposed area (charged area), carrying out development by allowing colorant (toner) to adhere to the charged area, transferring the colorant (toner) adhering to the charged area to an image receiving medium such as paper or other materials to form a pattern represented by the selectively exposed area on an image receiving medium such as paper or the like.
Conventional electrophotographic techniques can be roughly classified to a technique utilizing electrostatic latent images (xerographic process, Carlson process), a technique utilizing persistent internal polarization state and a technique utilizing persistent conductivity state.
The respective techniques will be briefly explained.
(a) Technique utilizing electrostatic latent images:
This is a technique for obtaining copies by repeating a series of steps of charging-imagewise exposure (formation of electrostatic latent images)-development (attraction of colorant)-transfer-fixation, using a selenium plate (selenium drum). This technique requires one imagewise exposure for obtaining every one copy.
(b) Technique utilizing persistent internal polarization state:
This is a technique according to which a plate-like material comprising ZnS:CdS phosphor and anthracene which has been applied with electrical field on both sides is subjected to imagewise exposure and carriers from which charges are removed by the above exposure are trapped in traps present in the plate-like material comprising ZnS:CdS phosphor and anthracene, thereby to form internal polarization and this internal polarization is retained even after electrical field and exposure are removed and thus internal polarization latent images are formed utilizing this persistent internal polarization state and the internal polarization latent images are developed and then the developed latent images are transferred to paper or the like to obtain a copy.
(c) Technique utilizing persistent conductivity state:
This is a technique according to which a layered material comprising a photoconductive layer prepared by dispersing an inorganic photoconductor powder such as zinc oxide, cadmium sulfide or the like in a resin, a photoconductive layer prepared by dispersing an organic photoconductor powder such as leuco-malachite green in a resin, a photoconductive layer prepared by adding leuco-malachite green (LMG) to a poly-N-vinylcarbazole (PVK) 2,4,7-trinitrofluorenone (TNF) carrier transport complex type photoconductor, or a photoconductive layer prepared by adding a diazonium salt (DS) to a poly-N-vinylcarbazole (PVK) 2,4,7-trinitrofluorenone (TNF) carrier transport complex type photoconductor, a switching layer prepared by dispersing Cu.TCNQ complex in a polymer which is formed on the photoconductive layer, and a photoconductive layer comprising PVK.TeNF(2,4,5,7-tetranitrofluorenone)carrier transport complex photoconductor is irradiated with light or the like, whereby there occurs difference in conductivity between exposed area and unexposed area and this difference in conductivity persistently remains even after termination of exposure to form latent conductivity images, which are developed and transferred to paper or the like to obtain a copy.
Electrophotographic photoreceptors are media for transfer of pattern used in electrophotographic method in which difference in physical or chemical state occurs between exposed area and unexposed area upon irradiation with light and correspond to the selenium plate (selenium drum), the plate-like material comprising ZnS:CdS phosphor and anthracene, and the layered material comprising a photoconductive layer comprising PVK.TeNF (2,4,5,7-tetranitrofluorenone) carrier transport complex photoconductor or other photoconductive layer, a switching layer and a carrier generation layer in the above-mentioned techniques (a), (b) and (c).
Among the above three electrophotographies, xerographic method and Carlson method have no memorization property and require one imagewise exposure for every one copying.
On the other hand, the technique using persistent internal polarization state and the technique using persistent conductivity state both utilize memorizability of photoreceptor and so do not require one imagewise exposure for every one copying, but these are still in the stage of technical development and have the problems such as low stability, insufficient sensitivity and resolution and poor tone reproduction (realization of halftone is difficult and shade of color becomes extreme, resulting in only image of deep color or colorless image). Thus, further improvement in these respects has been desired.
Therefore, electrophotographic photoreceptors excellent in stability, sensitivity, resolution and tone reproduction and having memorizability have been strongly demanded.